A Bio-Inspired Solid-Waste Recycling Strategy: Construction of Fluoride-Free, Fly Ash-Based, and Superhydrophobic...

To address the critical issues of fire risk and surface performance in steel structures, functionalized coatings were emerged as one of the most effective strategies. Inspired by the unique wettability of natural organisms, a superhydrophobic multifunctional coating was developed that simultaneously achieved fire protection and surface functionality. A hydrophobic fly ash-based hybrid flame retardant (SR-FPC@ZIF-67) was synthesized through sequential deposition of a phytic acid/cationic starch complex, ZIF-67, and silicone resin onto fly ash particles. The coating composed of silica nanoparticles, epoxy resin/polydimethoxysilane, and flame retardant was applied to steel surfaces via a one-step air-spraying technique. The resulting coating exhibited strong water repellency and low water adhesion. This superhydrophobicity endowed the coated steel with some multifunctional surface properties. Furthermore, the superhydrophobicity was maintained above 150° after 10 m of abrasion, 60 tape-peeling cycles, 48 h of acid/alkali immersion, and 48 h of UV irradiation. It demonstrated mechanical robustness, chemical stability, and weather resistance. Owing to the synergistic flame-retardant effect, the coated steel plates achieved a low back surface temperature of 258.8 °C after the fire ablation process, with a 51% reduction in total heat release. This fire resistance was attributed to the char-forming ability of the PA/CS complex, the catalytic charring effect of ZIF-67, and the physical barrier function of fly ash. Overall, this study provided a sustainable and effective approach to simultaneously resolving the fire protection and surface performance limitations of steel structures, while also opening a pathway for the value-added utilization of hazardous fly ash. This offered both theoretical insights and technical references for next-generation green multifunctional protective coatings.